The present invention relates generally to optical elements for laser systems, and more particularly to a high performance wavelength stabilizing laser mirror having utility in stabilizing a laser cavity within a narrow bandwidth.
Certain laser types are capable of operating over a broad wavelength band. For example, carbon dioxide (CO.sub.2) lasers are capable of lasing at several discrete wavelengths between 9.2 and 11.2 microns, but are usually configured to operate at 10.6 microns. Some CO.sub.2 lasers, such as RF-waveguide lasers with short cavities, modulate between wavelengths, which results in undesirable frequency and power modulations. In high power CO.sub.2 laser applications, gratings may not be suitable for wavelength stabilization because of a susceptibility of the grating to damage. Alexandrite lasers are capable of operating efficiently at various wavelengths between 700 and 800 nm at temperatures to about 80.degree. C. A standard fixed wavelength laser cavity (without a tuning element) having a broad-band rear cavity mirror will typically shift in wavelength of operation as the laser warms up. If the wavelength shifts to 769 nm, certain optical elements used in the cavities (such as folding prisms, polarizers and waveplates) may be damaged because of optical absorption in oxide glasses at 769 nm. Conventional narrow-band laser mirrors are generally fabricated using dielectric stack and/or metal coating technology, and have an unacceptably wide bandwidth (typically 10% or more) relative to the tuning range of both the CO.sub.2 and Alexandrite lasers.
The invention solves or substantially reduces in critical importance problems with prior art laser mirrors as just suggested by providing a laser cavity mirror or output coupler for stabilizing a laser within a narrow wavelength band, and is fabricated as an optical interference device in which the index of refraction is selectively continuously modulated between high and low values rather than in discrete steps as in conventional devices comprising dielectric layers. A laser may therefore be wavelength stabilized without using additional wavelength stabilization optics, such as an etalon, tuning plates, prism or grating. The invention may be used in high power laser applications to avoid damage to optical elements, has greater efficiency than conventional grating devices, is relatively inexpensive and may be fabricated with greater than 99% reflectivity and very narrow bandwidths (about 1% of center wavelength), whereas typical master gratings used for tuning a CO.sub.2 laser have grating efficiencies of 85 to 90%.
It is therefore a principal object of the invention to provide a wavelength stabilizing laser mirror or output coupler.
It is a further object of the invention to provide a laser mirror/laser output coupler for stabilizing a laser cavity within a narrow bandwidth.
It is yet another object of the invention to provide a low-cost, high-performance mirror/output coupler for stabilizing a laser cavity within a narrow bandwidth.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.